Film forming synthetic latexes comprising copolymer sulfonates and method of making same



FORMING SYNTHETIC LATEXES COMPRIS- ING COPOLYMER SULFONATES AND METHODOF MAKING SAME No Drawing. Original application March 30, 1956, SerialNo. 574,946. Divided and this application July 29, 1958, Serial No.751,639

20 Claims. (Cl. 260-295)" This invention concerns certain newfilm-forming synthetic latexes and a method of making the same. Thepresent application is a division of, and a substitute for, a copendingapplication of the same inventors, Serial No. 574,946, filed March 30,1956, and now abandoned.

The synthetic latexes which are provided by the invention are aqueousdispersions of copolymers of one or more aliphatic conjugated diolefineswith at least two monovinyl aromatic compounds, including a monovinylaromatic sulfonate, and an unsulfonated monovinyl aro matic compoundsuch as amonovinyl aromatic hydrocarbon or a nuclear halogenatedmonovinyl aromatic hyhydrocarbon. These aqueous dispersions, orcolloidal solutions, of the copolymers can be prepared in the presenceor absence of conventional emulsifying agents. They are exceptionallystable against coagulation by freezing and thawing or by addition ofsoluble inorganic salts such as sodium chloride, potassium chloride,sodium sulfate, potassium sulfate, or calcium chloride, etc. Thesesynthetic latexes can be spread in thin layers on solid surfaces, e.g.of wood, iglass, metals, etc., and dried to obtain adherent continuousfilms of the copolymers. When dried, the films can readily be removedfrom the;'base members by washing or scrubbing with water. Accordingly,these synthetic latexes are useful as coating compositions for thecasting and forming, on supporting surfaces, of adherent, but readilyremovable, protective films of the copolymers. Conventional additivessuch as dyes or pigments, plasticizers, thickening agents, etc., can beadmixed with these synthetic latexes to form water-base paints or othermodified coating compositions. Paints thus-prepared can be applied to,and dried-on, surfaces of Wood, glass, or metal, etc., to obtaindecorative coatings that can be removed, when desired, by washing withwater. Such removable paints can be used for the temporary decoration ofstore windows, etc.

The colloidally dispersed polymeric ingredients of these e tes P tent i2,913,429 Patented Nov. 17, 1959 ice form the copolymers, together witha water soluble polymerization catalyst and suflicient water to dissolvethe water-soluble catalyst and the vinyl aromatic sulfonate. It isessential, in order to obtain a copolymer latex of good' quality, thatthe polymerization mixture include a highly ionizable, Water-solublesalt, e.g. having an ionization constant of 10- or higher, such assodium chloride, potassium chloride, calcium chloride, sodium sulfate,potassium sulfate, sodium bromide, or potassium bromide, etc. .Alkalinitrites are preferably excluded from the mixture since they function aspolymerization inhibitors and in this respect differ from other saltssuch as' those just mentioned. Such ionizable salts other than nitritesappear to serve as catalyst, or catalyst promoters, for formation of thecopolymers by reaction of the nonhomogeneous mixture. The presence ofsodium bromide in amount corresponding to at least 0.25 percent of theweight of the vinyl aromatic sulfonate, or of a chemically equivalentamount of other highly ionized water-soluble inorganic salts, such asthose just mentioned, is usually suflicient for the purpose. Theionizable inorganic salts can be present in amounts as great as 15percent or more of the weight of the vinyl aromatic sulfonates. Sodiump-styrene sulfonate usually contains, as an impurity, sufficient of analkali metal halide or an alkaline earth metal halide, e.g.- NaBr, KBr,CaBr or a corresponding metal chloride, to serve the purpose.

- water-soluble polymerization catalysts are sodium persynthetic latexesare copolymersof a total of from 4 to l 35, preferably from 5 to 15,Weight percent of one or more monovinyl aromatic sulfonates, a total offrom 5 to 40, preferably from 20 to 40, weight percent of either or bothof the compounds, 1,3-butadiene and isoprene, and

a total of from 93 to 25, preferably from 77 to 45, percent of one ormore unsulfonated monovinyl aromatic compounds such as styrene,ar-vinyltoluene, ar-monochlorostyrene, and a-r-dichlorostyrene, etc. Anysalt of an ar-monovinyl aromatic sulfonic acid, which salt can bedissolved in water to form a solution containing at sulfate, potassiumpersulfate, and ammonium persulfate,

etc. Examples of suitable oil-soluble polymerization catalysts are theorganic peroxy compounds such as dibenzoyl peroxide, or dilauroylperoxide, etc. Mixtures of the alkali persulfates and the oil-solubleorganic peroxides ar'ehighly efiective and are preferred. A mixture ofabout equal weights of an alkali persulfate and an organic peroxide suchas dibenzoyl peroxide or dilauroyl peroxide is preferred. The mixedcatalyst is more active and apparently has less tendency to cause, orpermit, coagulation of the copolymer product than the watersolublecatalyst alone. An amount of catalyst corresponding to from 0.1 to 2,preferably from 0.5 to 1, percent of the combined weight of thepolymerizable compounds is usually employed. The catalyst can be used inlarger proportions if desired.

A mixture of these several starting materials, in the relativeproportions above-indicated, can be heated, e.g'. at temperatures offrom 40 to 120 C., preferably from 60 to C., to form a latex of thecolloidally dispersed copolymer. A portion of the copolymer sometimescoagulates as a button during the polymerization reaction. I r Thepolymerization is advantageously accomplished in the absence ofconventional emulsifying agents, but any of the usual emulsifying:agents can be added, if desired.

It has been found that the amount of button formed decreases withincrease in the proportion of water present. There is'also less tendencytoward button formation when using a mixture of water-soluble andoil-soluble polymerization catalysts than when using either suchcatalyst alone.

The polymerization is preferably carried out while preventing freeaccess of air to the mixture. For instance, it can be accomplished in aclosed vessel such as a bomb or autoclave. Any air is preferably sweptfrom the vessel with an inert gas or vapor such as nitrogen, or helium,etc., prior to carrying out the polymerization. The polymerization isoften carried out in a manner such as to avoid formation of a latexcontaining more than 25 weight percent of the copolymer, since it hasbeen observed that the tendency toward coagulation of the copolymerbecomes greater when the copolymer is formed at higher concentrations.However, it is possible, by careful choice of the polymerizationconditions, to form a latex containing more than 40 Weight percent ofthe copolymer without coagulation occurring to more than a minor extent.The formation of a latex of higher concentration than desired can beavoided by use of a sulficiently large proportion of water in thepolymerization mixture, or by terminating the reaction when thecopolymer has been formed in the desired concentration.

After carrying out the polymerization to the desired extent, the vesselis opened, and any coagulated polymeric material is removed, egg. byfiltering r decanting, from the copolymer latex product. Any unconsumedmonomeric material, if present, can be vaporized from the latex.

The copolymer latexes thus obtained are exceptionally stable againstcoagulation. For instance, latexes prepared under the preferredconditions hereinbefore described can be frozen and thawed or can betreated with half of their volume of an aqueous 10 weight percentcalcium chloride solution without coagulating the copolymer ingredientthereof. The latexes can be spread as a thin layer and dried'on asupporting surface, e.g. of g'lass, steel, or. wood, to obtain adherentcontinuous films of the copolymers.

The following examples describe ways of practicing the invention andillustrate certain of its advantages, but are not to be construed aslimiting its scope.

. EXAMPLE 1.

- To a frozen mixture of 125 parts by weight of water, 78 parts ofstyrene, parts of sodium p-styrene sulfonate containing from 1 to 2weight percent of sodium bromide, 0.4. part of sodium bicarbonate, 0.8part of sodium persulfate and 0.64 part of sodium meta-bisulfite therewas added 42 parts of liquefied butadiene. Air was swept, by a stream ofnitrogen, from the vessel contain-' ing the mixture and the vessel wasclosed. The vessel and its contents were warmed to 70 C. and shakenwhile at that temperature for 24 hours. The vessel was then opened, anda minor amount of the butadiene, that re} mained unconsumed, was vented.Also, about 27 grams of solid polymeric material that had formed andagglomerated 'was removed. The remaining product was a latex, i.e. anaqueous colloidal solution, which contained approximately 39 weightpercent of the dispersed co.- polymer product. A portion of the latex,when spread as a thin layer on a glass plate, dried to form a tightlyadhering, clear, transparent film of the coplymer. Another portion ofthe latex was frozen andthawed four times without coagulating thecopolymer ingredient. 'An addition of a concentrated aqueous calciumchloride solution to a portion of the latex in amount such that theresulting solution contains percent by weight of calcium chloride doesnot cause coagulation of the copolymer ingredient. I

EXAMPLE 2 In each of three experiments, the amount of sodium p-sty'renesulfonate, of about 95 Weight percent purity, indicated in the followingtable was dissolved in 120 parts by weight of water. The sodiump-styrene sulfonate contained from l to 2 percent by weight of sodiumbromide as an impurity. To the solution there were added styrene in theamount indicated in the table and 0.3 part by weight of sodiumpersulfate and 0.3 part of'benzoyl peroxide. Air was swept by nitrogenfrom a glass vessel containing the mixture and 24 parts by weight of1,3-

butadiene was added 'tothe mixture. The vessel was then I closed and wasshaken and heated at 75 C. for '18 hours. The vessel was then cooled andopened and the reaction mixture was removed. The mixture comprised anaqueous latex of a colloidally dispersed copolymer of styrene,butadiene, and sodium styrene sulfonate together with a body, or button,of a coagulated portion 5 of the copolymer. The wet button was removedand weighed. A portion of the remaining latex was analyzed to determinethe solids content thereof, which corresponds approximately to thepercent by weight of copolymer product dispersed therein. Table I givesthe parts by weight of styrene and of sodium p-styrene sulfonate presentin each of the starting mixtures. It also gives the parts by weightof'wet copolymer button that was removed from the reaction mixture ineach experiment and the solids content of the remaining aqueouscopolymer EXAMPLE 3 In each of a number of experiments a mixture of 0.44part by weight of sodium persulfate, 0.42 part of sodium bicarbonate,0.05 part of the sodium salt of N,N- ethylenediaminetetracetic acid, andstyrene, 1,3-butadiene, sodium p-styrene sulfonate and water in therespective-amounts hereinafter indicated, was heated at 70 C. under anatmosphere of nitrogen in a closed vessel for 24 hours. The sodiumstyrene sulfonate contained from '1 to 2 percent of sodium bromide as animpurity. A latex of a copolymer of styrene, butadiene, and sodiumstyrene sulfonate, in approximately the same'relative prop'ortions as inthe starting mixture, was obtained. All of the copolymer was dispersedas'colloidal particles in the latex, i.e. no button of coagulatedpolymeric material was obtained. Each latex contained between and 25percent of the copolymer in the form of particles having anyaveragediameter of about 1800 Angstrom units. TablelI'gives the parts by weightof water and of the respective polymerizable starting materialsemployedin each experiment. In the table, water and butadiene aredesignated by their formulas and sodium styrene sulfonate In'eachofseveral experiments, a stainless steel bomb was charged with 500 partsby weight of water, 312 parts of styrene, 168 parts of butadiene, 21parts of sodium p-styrene sulfonate, 2.5 parts of sodium bicarbonate,and

with the amounts of sodium persulfate, benzoyl peroxide and sodiumbromide indicated in Table IH. In charging the bomb, the ingredientsother than butadiene were introduced and air was swept from the bombwith nitrogen. The butadiene was then added and the bomb was closed. Thebomb was shaken and heated at 70 C. and, at measured intervals, aliquotportions of the resulting copolymer latex were withdrawn through avalved outlet and tested to determine the percent by weight oi theresulting copolymer of styrene, butadiene and sodium styrene sulcEonatecolloidally dispersed therein. Incertain of the experiments at one hourintervals afterthe start of the polymerization, there were added, byinjection through a valved inlet under pressure, four successiveportions of an aqueous sodium persulfate solution, each of whichportions consisted of 1 part by weight of sodium persulfate in parts ofwater. After completing each experiment, the bomb was cooled, opened,and any coagulated polymeric material, i.e. any of the so-called button,was removed from the reaction mixture, squeezed to remove adsorbed latextherefrom, and weighed. Also, the percent by weight of colloidallydispersed polymer in the latex product was determined after completingthe experiment. The following table gives the parts by weight of benzoylperoxide, sodium persulfate, and of sodium bromide present in each ofthe starting mixtures. It indicates the experiments in which addedportions of an aqueous sodium persulfate solution were introduced byinjection under pressure during the polymerization. The table also givesthe time in hours after the start of each polymerization reaction atwhich a sample of the latex product was withdrawn for testing and itgives the weight percent of dispersed copolymer in the sample. The tablefurther gives the total hours of heating at 70 C. in carrying out eachpolymerization; theamount of copolymer button formed, expressed aspercent of the combined weight of styrene, butadiene and sodiumstysulting decrease in concentration of colloidally dispersed copolymerin the final latex product. Run 3, as compared with run 2, shows that byincreasing the propor- EXAMPLE s In each of a series of experiments amixture of 120 parts by weight of water, 4 parts of sodium p-st'yrenesulfonate containing from 1 to 2'percent by weight of sodium bromide,0.3 part of sodium persultate; 0.3 part of benzoyl peroxide, and theamounts of styrene and of'1,3- butadiene indicated in the followingtable was agitated and heated at 70 C. in contact with nitrogen in aclosed vessel for 18 hours. The'vessel was then opened and the chargeremoved. The reacted mixture was a latex of the colloidally dispersedcopolymer together with a button of coagulated copolymer. The button wasremoved, absorbed latex was squeezed therefrom, and the button wasweighed. The remaining latexwas tested to determine its solids content.The following table gives the parts by weight of styrene and ofbutadiene, in each of the starting mixtures. It gives the amount ofcopolymer button, expressed as percent of the combined weight of thepolymerizable starting materials. It also gives the percent by weight ofcolloidally dispersed copolymer in the latex product.

rene sulfonate initially charged to the bomb, and the per- Table IV centby weight of colloidally dispersed copolymer 1n the 4-0 final latexproduct. In the table benzoyl peroxide 18 ab- 1 Starting M1xture Resultsbreviated as B2 0 Cmpnses Run No. Styrene, CtH Percent Percent Table IIIPts. Pts. Button 00110.0!

Latex Starting Mixture NanSzOa Percent -72 4 56.3 41 Comprises addedTime solids Percent 68 8 43.8 39 R n during of samin latex Button 64 1242.5 37 N polymerpling, when Formed 16 37.5 36 B2201, Nazsgos, NaBr,ization Hrs. sam- 48 28 37.5 35 Pts. Pts. Pts. pled 44 32 37. 5 35 1None 5 0.5 No 2115 910 III: EXAMPLE6 24.0 16.0 8- F3 55 In each of anumber of experiments, a mixture of 10.0 18.1 Water, Lil-butadiene, thevinyl aromatic. compound indi- 2 None 1 0.5 Yes--- gig 3;; cated in thefollowing table, the salt of p-styrene sulfo- 32.2 3.1 nate which isalso indicated, benzoyl peroxide and sodi- 1 um persulfate was subjectedto polymerization by agi- 3 None 1 2. 45 Yes mi 3% 2:3 tating andheating the same in contact with nitrogen in a 21.5 20.8 0.0 closedvessel at the temperature and for the time given 2 31% in Table V. Thevessel was then cooled, opened, and 4 5 5 2. 45 N0 17.5 43.5 the weightpercent solids content of the resulting latex 19.0 44.0 2 of the severalpolymerizable starting materials was de- In each of the runs 1-3 of theabove table, sodium persulfate, a water-soluble compound, was used asthe only polymerization catalyst. From a comparison of run 2 with run 1it will be seen that the portionwise addition of the sodium persulfatecatalyst during the polymerization caused an increase in the rate ofpolymerization, but also caused a large increase in the proportion ofthe copolymer product which becarne'coagulated and a retermined. Thetable identifies andgives the proportions, as parts by weight, of theseveral starting materials. .The catalyst which is referred to is amixture of equal parts by weight of benzoyl peroxide andsodiumpersulfate. It also gives the solids content, expressed as percent byweight of the latex product. This corresponds approximately to thepercent by weight of the colloidally dispersed copolymer in the latex.The copolymer is that of the polymerizable" starting materials in aboutthe relative proportions in which they we're employed.

' Table V Starting Mixture Y Polymerization Conditions Latex, Percent fRun v Solids N o. Vlny1 Aromatic Compound Styrene Sulfonate Con- H2C4Hu, Catalyst, Time, Temp., tent 7 Pts. Pts. Pts. Hrs. O. I Kind Pts.Kind Pts.

120 2,5-dlchlorostyrene 48 4 0.6 18- I 75 20 120 16: -d0 60 4 0.6 -18 7518 120 28 Vinyltoluene 48 4 0.6 18 75 18 140 15 Styrene 42 3 g 0.6 v 718 75 28 120 a 48 @gffia ssgfia; i 0.6 v m I so a "We claim: a copolymerof styrene, butadiene and sodium p-styrene l. A coating compositionComprising an aqueous colloidal dispersion of a copolymer of between 4and 35 percent by weight ofat least one water-soluble salt of anar-rnonovinyl aromatic monosulfonic acid, from 5 to 40 percent of atleast one aliphatic conjugated diolefine containing-from 4-to 5 :Carbonatoms in the molecule and having only 4 carbonatomsin a chain of themolecule, and from 93 to 25 percent of at least one unsulfonatedmonovinyl aromatic compound of the class consisting of vinyl aromatichydrocarbons and nuclear halogenated vinyl aromatic hydrocarbons.

2. A coating composition comprising 21 aqueous colloidal dispersion ofarcopolymer of between 5 and percent by weight of at least onewater-soluble salt of an ar-monovinyl aromatic monosulfonic acid, fromto 40 percent .of a least one'aliphatic conjugated diolefine containingfrom 4 to 5 carbon atoms in the molecule and having only 4 carbon atomsin a chain of the molecule, and from 77 to45 percent of at least oneunsulfonated monovinyl aromatic compound of the class consisting ofvinyl aromatic hydrocarbons. and nuclear halogenated vinyl aromatichydrocarbons; which composition can be frozen and thawed and can betreated with at least half its volume of an aqueous 10 percent calciumchloride solution 'without becoming coagulated.

3. A coating 1 composition, as claimed in claim 2, whe'rein;thecopolymer ingredient consists essentially of a copolymer oflstyrene,butadiene and a water-soluble salt ofan ar-styrene sulfonicacid.

4. A coating composition, as claimed in claim 2, wherein the copolymeringredient consists essentially of a copolymer of styrene, butadiene,and sodium p-styrene sulfonate. a

5. A coating composition, as claimed in claim '2, wherein the copolymeringredient consists essentially of a copolymer of vinyltoluene,vbutadiene, and sodium p-styrene sulfonate.

6. A. coating composition, as claimed in claim 2, wherein the copolymeringredient consists essentially of a 'copolymerof 2,5-dichlorostyrene,butadiene and sodium p-styrene sulfonate.

7. A coating composition, as claimed in claim 2, wherein the copolymeringredient consists essentially of a copolymer of styrene, butadiene andcalcium p-styrene sulfonate.

8. A coating composition, as claimed in claim 2, wherein thecopolymeringredient consists essentially of a copolymer of styrene, butadiene,triethylammonium pstyrene sulfonate, and'sodium p-styrene sulfonate.

9. A coating composition, as claimed in claim 2, consisting essentiallyof an aqueous colloidal solution, of the copolymer, that issubstantially free of added emulsifying agents. v

10. A'coating'composition, as claimed in claim 9, wherein the copolymeringredient consists essentially of a copolymer of styrene, butadiene anda water-soluble salt of an ar-vinyl aromatic sulfonic acid.

11. A coating composition, as claimed in claim 9, wherein the copolymeringredient consists essentially of sulfonate. I

12. A coating composition, as claimed in claim 9, wherein the copolymeringredient consists essentially of a copolymer of vinyltoluene,butadiene, and a water-soluble salt of an ar-vinyl' aromatic sulfonicacid.

13. A coating composition, as claimed in claim 9, wherein the copolymeringredient consists essentially'of a copolymer of vinyltoluene,butadiene and sodium pstyrene sulfonate.

14. A coating composition, as claimed in claim 9, wherein the copolymeringredient consists essentially of a copolymer of 2,5-dichlorostyrene,butadiene and sodium p-styrene sulfonate. l

15. A coating composition; as claimed in claim 9, wherein the copolymeringredient consists essentially of a copolymer of styrene, butadiene andcalcium p-styrene sulfonate. i

16. A coating composition, as claimed in claim 9, wherein the copolymeringredient-consists essentially of a copolymer of styrene, hutadiene,triethylammonium pstyrene 'sulfonate and'sodinm p-styrene sulfonate.

, 17. A method of making a stable, film-forming aqueous copolymerdispersion that is effective as a coating composition, which methodcomprises agitating and heating at a polymerization temperature in thesubstantial absence of air, a mixture of from 4 to 35 percent by weightof at least one ar-vinyl aromatic monosulfonate that is sulficientlysoluble in water to permit formation at room temperature of an aqueousweight percent solution there-, of, from 20 to 40 percent of analiphatic conjugated diolefine containing from 4 to 5 carbon atoms inthe molecule and having only 4 carbon atoms in a chain of the molecule,and from'25 to 78 percent of an unsulfonated monovinyl aromatic compoundof the class consisting ofvinyl aromatic hydrocarbons and nuclear halogenated vinyl aromatic hydrocarbons that is free of reactive groupsother than the vinyl radical, the proportions just expressed being basedon the combined weight of the above-mentioned polymerizable startingmaterials, together with water, a water-soluble alkali persulfate as apolymerization catalyst and an amount of other watersoluble andionizable inorganic salt chemically equivalent to the presence of sodiumbromide in a proportion corresponding to atleast 0.25 percent of theweight of the vinyl aromatic sulfonate, said other ionizable inorganicsalt having an ionization constant at least as high as 10 and saidalkali persulfate, other ionizable inorganic salt and the ar-vinylaromatic sulfonate being present as an aqueous solution thereof, and thepolymerization catalyst being employed in a proportion corresponding tofrom 0.1 to 2 percent of the combined weight of the above-mentionedaliphatic conjugated diolefine and vinyl aromatic compounds.

18. A method, as claimed in claim 17, wherein an organic peroxidecontaining the peroxy group as the only functional group in the moleculeis also initially added, as a polymerization catalyst, to thepolymerization mixture and the latter is substantially free of addedemulsifying agents.

19. A method, as claimed in claim 18, wherein the ingredient and anoil-so1uble organic peroxide containing polymerization mixture initiallycomprises a water-soluthe peroxy group as the only functional group inthe ble and ionizable metal bromide in amount correspondmolecule is alsopresent, as a polymerization catalyst, in ing to from about 0.25 toabout 15 percent of the weight the polymerization mixture during thepolymerization of the vinyl aromatic sulfonate. 5 reaction. 1

20. A method, as claimed in claim 18, wherein so- No references cited.drum brom1de is present as an romzable morgamc salt

1. A COATING COMPOSITION COMPRISING AN AQUEOUS COLLOIDAL DISPERSION OF ACOPOLYMER OF BETWEEN 4 AND 35 PERCENT BY WEIGHT OF AT LEAST ONEWATER-SOLUBLE SALT OF AN AR-MONOVINYL AROMATIC MONOSULFONIC ACID, FROM 5TO 40 PERCENT OF AT LEAST ONE ALIPHATIC CONJUGATED DIOLEFINE CONTAININGFROM 4 TO 5 CARBON ATOMS IN THE MOLECULE AND HAVING ONLY 4 CARBON ATOMSIN A CHAIN OF THE MOLECULE, AND FROM 93 TO 25 PERCENT OF AT LEAST ONEUNSULFONATED MONOVINYL AROMATIC COMPOUND OF THE CLASS CONSISTING OFVINYL AROMATIC HYDROCARBONS AND NUCLEAR HALOGENATED VINYL AROMATICHYDROCARDONS.